A resonator used for this type of conventional angular velocity sensor for example had a structure as shown in FIG. 8 and FIG. 9. FIG. 8 is a perspective view illustrating a resonator used in a conventional angular velocity sensor for example. FIG. 9 is a sectional side view illustrating a vibration element in the resonator.
As shown in FIG. 8 and FIG. 9, vibration element 1 is composed of diaphragm 2; piezoelectric body layer 3 consisting of zinc oxide that is provided on an upper face of diaphragm 2; and upper electrode layer 4 consisting of Ti and Ni that is provided on an upper face of piezoelectric body layer 3. Support section 5 supports vibration element 1. Spacers 6 support vibration element 1 from upper and lower sides. Dumet wires 7 support spacers 6 from upper and lower sides. Glass tube 8 is welded to surround the periphery of dumet wire 7 and the interior of dumet wire 7 is filled with oxygen gas of 10 KPa to 30 KPa.
When vibration element 1 is subjected to a high temperature for melting glass tube 8 in a step of producing vibration element 1 in a resonator used in a conventional angular velocity sensor for example, upper electrode layer 4 formed on piezoelectric body layer 3 deprives piezoelectric body layer 3 of oxygen. This causes piezoelectric body layer 3 to show a conductive property, preventing piezoelectric body layer 3 from functioning as a piezoelectric body. To prevent this, a conventional resonator has been structured so that oxygen gas is filled in the interior of dumet wire 7 to prevent piezoelectric body layer 3 from being deprived of oxygen gas.
In the case of the conventional angular velocity sensor, when a substance other than piezoelectric body layer 3 reacts with oxygen gas in dumet wire 7 to generate carbon dioxide gas, an increased molecular weight causes an increase in the pressure in dumet wire 7 from 10 kPa to 30 kPa, for example, showing an increase of 20 kPa.
When a driving efficiency of an angular velocity sensor is defined to have a value obtained by dividing a driving voltage by a monitor voltage, the driving efficiency of 1 (one) corresponding to the internal pressure of dumet wire 7 of 10 kPa varies to 1.4 when the internal pressure of dumet wire 7 is 30 kPa.
The technique as described above is disclosed by background art publications such as International Publication Number WO 03/046479 (pamphlet), Japanese Patent Unexamined Publication No. S64-29706, and Japanese Patent Unexamined Publication No. S62-183147.
In the above conventional structure, oxygen gas of 10 kPa to 30 kPa is filled in dumet wire 7 and thus an initial molecular weight in dumet wire 7 is small to enable a small driving resistance by the oxygen gas of vibration element 1. However, when the reaction with oxygen gas causes carbon dioxide gas, the molecular weight in dumet wire 7 is increased to cause an increased driving resistance of vibration element 1, which causes a disadvantage of a significant change in the driving efficiency of vibration element 1.